electron/docs/tutorial/planned-breaking-changes.md

# Planned Breaking API Changes (4.0)

The following list includes the APIs that will be removed in Electron 4.0.

There is no timetable for when this release will occur but deprecation
warnings will be added at least [one major version](electron-versioning.md#semver) beforehand.

## `webFrame`

```js
// Deprecated
webFrame.registerURLSchemeAsPrivileged('app', {secure: true})
// Replace with
protocol.registerStandardSchemes(['app'], {secure: true})
```

*Nota Bene:* Before we can remove this we need to update all of the relevant specs to `protocol.registerStandardSchemes(['app'], {secure: true})`.

## `app.makeSingleInstance`

```js
// Deprecated
app.makeSingleInstance(function (argv, cwd) {

})
// Replace with
app.requestSingleInstanceLock()
app.on('second-instance', function (argv, cwd) {

})
```

## `app.releaseSingleInstance`

```js
// Deprecated
app.releaseSingleInstance()
// Replace with
app.releaseSingleInstanceLock()
```

## `FIXME` comments

The `FIXME` string is used in code comments to denote things that should be
fixed for the 3.0 release. See
https://github.com/electron/electron/search?q=fixme